The present invention relates to a process for pleating meltblown media, and more specifically, to the use of ultrasonic bonding to impart additional stiffness to meltblown media, thereby enabling pleating. Although the present invention was developed for use in filter devices, certain applications may lie outside of this field.
Meltblown media lack the necessary physical properties that would allow the successful pleating of the media. To enable pleating, meltblown media are usually bonded to a wire screen or to cellulose media. The use of such wire screen or cellulose backing has several disadvantages such as additional material costs, additional weight, slower production of pleats, and potential problems during pleating. For example, when meltblown media backed with a woven wire screen is put through a pleater, the screen may get caught and torn by the pleater. Various methods, including saturating the media with a resin to provide improved stiffness, have been proposed to render meltblown media pleatable.
Hence, the need exists for a process by which meltblown media is made pleatable at higher production rates and reduced cost over the current use of the wire screen and cellulose backing processes. The present invention satisfies this need in a novel and non-obvious way.
One aspect of the invention described herein is the use of ultrasonic bonding to create additional stiffness in a meltblown web in the machine direction. A heated score bar or ultrasonic horn can then be used to deform the meltblown web and lock in the pleat structure.
One form of the present invention contemplates the use of ultrasonic bonding wheels to create continuous linear bond lines in the machine direction as the meltblown web is being produced. A heated score bar or ultrasonic horn is used to raise the temperature of the web above its glass transition temperature and to deform the web to form the pleats.
In another form of the present invention, ribbons are laid down in the machine direction on the meltblown web and ultrasonically bonded thereto in order to enhance the stiffness of the web. The ribbons may be used alone or in conjunction with the linear bond lines.
Bond lines, either with or without the added ribbons, can be used in conjunction with resin saturation of the meltblown web to create even greater stiffness.
One object of the present invention is to provide a unique process of rendering meltblown media pleatable using ultrasonic bonding.